CN107442952B - Laser processing apparatus and method for producing GaN wafer - Google Patents

Laser processing apparatus and method for producing GaN wafer Download PDF

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Publication number
CN107442952B
CN107442952B CN201710341747.7A CN201710341747A CN107442952B CN 107442952 B CN107442952 B CN 107442952B CN 201710341747 A CN201710341747 A CN 201710341747A CN 107442952 B CN107442952 B CN 107442952B
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laser
gan
laser beam
pulse
sub
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CN107442952A (en
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平田和也
汤平泰吉
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Disco Corp
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Disco Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/0006—Working by laser beam, e.g. welding, cutting or boring taking account of the properties of the material involved
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/03—Observing, e.g. monitoring, the workpiece
    • B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/035—Aligning the laser beam
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
    • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/08—Devices involving relative movement between laser beam and workpiece
    • B23K26/0823—Devices involving rotation of the workpiece
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/08—Devices involving relative movement between laser beam and workpiece
    • B23K26/083—Devices involving movement of the workpiece in at least one axial direction
    • B23K26/0853—Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/08—Devices involving relative movement between laser beam and workpiece
    • B23K26/10—Devices involving relative movement between laser beam and workpiece using a fixed support, i.e. involving moving the laser beam
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36—Removing material
    • B23K26/362—Laser etching
    • B23K26/364—Laser etching for making a groove or trench, e.g. for scribing a break initiation groove
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36—Removing material
    • B23K26/38—Removing material by boring or cutting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36—Removing material
    • B23K26/40—Removing material taking account of the properties of the material involved
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/50—Working by transmitting the laser beam through or within the workpiece
    • B23K26/53—Working by transmitting the laser beam through or within the workpiece for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
    • C30B29/403—AIII-nitrides
    • C30B29/406—Gallium nitride
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
    • C30B33/06—Joining of crystals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02002—Preparing wafers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/26—Bombardment with radiation
    • H01L21/263—Bombardment with radiation with high-energy radiation
    • H01L21/268—Bombardment with radiation with high-energy radiation using electromagnetic radiation, e.g. laser radiation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67011—Apparatus for manufacture or treatment
    • H01L21/67092—Apparatus for mechanical treatment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
    • H01S3/10023—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by functional association of additional optical elements, e.g. filters, gratings, reflectors
    • H01S3/1003—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by functional association of additional optical elements, e.g. filters, gratings, reflectors tunable optical elements, e.g. acousto-optic filters, tunable gratings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2101/00—Articles made by soldering, welding or cutting
    • B23K2101/36—Electric or electronic devices
    • B23K2101/40—Semiconductor devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0085—Modulating the output, i.e. the laser beam is modulated outside the laser cavity

Abstract

Provided are a laser processing device and a GaN wafer production method, which can efficiently cut a GaN ingot to produce a GaN wafer. A laser processing apparatus for producing a GaN wafer from a GaN ingot, wherein the laser processing apparatus includes a laser beam irradiation unit that irradiates a laser beam having a wavelength that is transparent to the GaN ingot held on a chuck table. The laser beam irradiation unit includes a laser oscillator that oscillates a laser beam, the laser oscillator including: a laser light source that oscillates high-frequency pulse laser light; a thinning-out unit that thins out the high-frequency pulse oscillated by the laser light source at a predetermined repetition frequency and generates a 1-burst pulse using the high-frequency pulse as a sub-pulse; and an amplifier that amplifies the generated burst.

Description

Laser processing apparatus and method for producing GaN wafer
Technical Field
The present invention relates to a laser processing apparatus and a GaN wafer production method for producing a GaN wafer from a GaN ingot.
Background
A Si (silicon) wafer, on which a plurality of devices such as ICs and LSIs are formed on the front surface thereof and divided by planned dividing lines, is divided into device chips by a dicing apparatus or a laser processing apparatus, and the divided device chips are used in electronic devices such as mobile phones and personal computers.
Further, since the band gap of GaN (gallium nitride) is 3 times as wide as Si, it is known that a GaN wafer is used when forming devices such as power devices and LEDs, and the GaN wafer can be cut from a GaN ingot using an inner peripheral blade having a blade thickness thinner than an outer peripheral blade (see, for example, patent document 1).
Patent document 1: japanese patent laid-open publication No. 2011-84469
However, even if the wafers are sliced from the GaN ingot using the inner peripheral blade, since the thickness of the inner peripheral blade is about 0.3mm, for example, with respect to the thickness of the GaN wafer (for example, 150 μm), 60 to 70% of the GaN ingot is cut and discarded at the time of slicing, which is not economical.
Disclosure of Invention
Therefore, an object of the present invention is to provide a laser processing apparatus and a GaN wafer production method that can efficiently cut a GaN ingot to produce a GaN wafer.
According to one aspect of the present invention, there is provided a laser processing apparatus adapted to produce a GaN wafer from a GaN ingot, the laser processing apparatus comprising: a chuck table for holding an ingot; and a laser beam irradiation unit that irradiates a laser beam having a wavelength that is transparent to a GaN ingot held on the chuck table, the laser beam irradiation unit including: a laser oscillator that oscillates a laser beam; and a condenser for irradiating the GaN ingot with the laser beam oscillated from the laser oscillator while locating a condensing point thereof inside the GaN ingot, and forming a fracture layer at an interface having a depth corresponding to a thickness of a GaN wafer to be produced, the laser oscillator including: a laser light source that oscillates high-frequency pulse laser light; a thinning-out unit that thins out the high-frequency pulse oscillated from the laser light source at a predetermined repetition frequency and generates 1 burst pulse using the high-frequency pulse as a sub-pulse; and an amplifier that amplifies the generated burst.
The thinning-out section preferably thins out the number of sub-pulses, which is the longest of the 2 to 10 sub-pulses extending the destruction layer at the interface position where the focal point is located, to the number of sub-pulses constituting 1 burst pulse, and generates a burst pulse, and particularly preferably, the number of sub-pulses extending the longest of the destruction layer is 3.
According to another aspect of the present invention, there is provided a GaN wafer production method for producing a GaN wafer from a GaN ingot, the GaN wafer production method including the steps of: a holding step of holding the GaN ingot by a chuck table; a laser beam irradiation step of irradiating a GaN ingot held on the chuck table with a laser beam having a wavelength that is transparent to the GaN ingot while locating a converging point of the laser beam inside the GaN ingot, and forming a damaged layer on an interface having a depth corresponding to the thickness of a GaN wafer to be produced; and a wafer peeling step of peeling off the GaN wafer from the ingot, the laser oscillator for oscillating the laser beam including: a laser light source that oscillates high-frequency pulse laser light; a thinning-out unit that thins out the high-frequency pulse oscillated by the laser light source at a predetermined repetition frequency to generate 1 burst pulse using the plurality of high-frequency pulses as sub-pulses; and an amplifier that amplifies the generated burst.
The thinning-out section preferably thins out the number of sub-pulses, which is the longest of the 2 to 10 sub-pulses extending the destruction layer at the interface position where the focal point is located, to the number of sub-pulses constituting 1 burst pulse, and generates a burst pulse, and particularly preferably, the number of sub-pulses extending the longest of the destruction layer is 3.
The present invention is configured as described above, and the energy of 1 burst pulse is dispersed over the time width of 1 pulse and irradiated, thereby separating GaN into Ga and N in stages and efficiently forming a damaged layer.
Drawings
Fig. 1 is a perspective view of a laser processing apparatus having a laser oscillator according to an embodiment of the present invention.
Fig. 2 is a schematic block diagram showing a laser beam irradiation unit.
Fig. 3 (a), (b), and (c) are diagrams for explaining a method of setting the number of pulses of the high-frequency pulse constituting the burst pulse in the laser beam irradiation unit shown in fig. 2.
Fig. 4 (a) and (b) are perspective views showing a laser beam irradiation process.
Fig. 5 is a perspective view showing a wafer peeling process.
Description of the reference symbols
2: a laser processing device; 4: a base station; 6: a holding unit; 8: a mobile unit; 10: a laser beam irradiation unit; 12: a shooting unit; 16: a peeling unit; 60: a GaN ingot; 62: and a GaN wafer.
Detailed Description
Embodiments of a laser processing apparatus and a GaN wafer production method according to embodiments of the present invention will be described below in detail with reference to the drawings.
The laser processing apparatus 2 shown in fig. 1 includes: a base table 4; a holding unit 6 for holding a workpiece; a moving unit 8 that moves the holding unit 6; a laser beam irradiation unit 10; a photographing unit 12; a display unit 14; a peeling unit 16; and a control unit not shown.
The holding unit 6 includes: a rectangular X-direction movable plate 20 mounted on the base 4 to be movable in the X-direction; a rectangular Y-direction movable plate 22 mounted on the X-direction movable plate 20 to be movable in the Y-direction; and a cylindrical chuck table 24 rotatably mounted on the upper surface of the Y-direction movable plate 22. The X direction is a direction indicated by an arrow X in fig. 1, and the Y direction is a direction indicated by an arrow Y and is a direction perpendicular to the X direction. The plane defined by the X-direction and the Y-direction is substantially horizontal.
The moving unit 8 includes an X-direction moving unit 26, a Y-direction moving unit 28, and a rotating unit (not shown). The X-direction moving unit 26 includes: a ball screw 30 extending in the X direction on the base 4; and a motor 32 coupled to one end of the ball screw 30. A nut portion (not shown) of the ball screw 30 is fixed to a lower surface of the X-direction movable plate 20. The X-direction moving unit 26 converts the rotational motion of the motor 32 into linear motion by the ball screw 30 and transmits the linear motion to the X-direction movable plate 20, thereby moving the X-direction movable plate 20 forward and backward in the X direction along the guide rail 4a on the base 4. The Y-direction moving unit 28 includes: a ball screw 34 extending in the Y direction on the X-direction movable plate 20; and a motor 36 coupled to one end of the ball screw 34. A nut portion (not shown) of the ball screw 34 is fixed to a lower surface of the Y-direction movable plate 22. The Y-direction moving unit 28 converts the rotational motion of the motor 36 into a linear motion by the ball screw 34 and transmits the linear motion to the Y-direction movable plate 22, thereby moving the Y-direction movable plate 22 forward and backward in the Y direction along the guide rail 20a on the X-direction movable plate 20. The rotation unit includes a motor (not shown) built in the chuck table 24, and rotates the chuck table 24 with respect to the Y-direction movable plate 22.
The laser beam irradiation unit 10 is disposed in a housing 39, and includes a condenser 10a disposed on a front end lower surface of the housing 39, wherein the housing 39 is supported by a support member 38 extending upward from an upper surface of the base 4 and extends substantially horizontally.
The imaging unit 12 and the condenser 10a are disposed on the front end lower surface of the housing 39 with a space in the X direction. The shooting unit 12 includes: a normal imaging element (CCD) that performs imaging by visible light; an infrared irradiation unit that irradiates infrared rays onto a workpiece; an optical system for capturing infrared rays irradiated by the infrared irradiation unit; and an imaging element (infrared CCD) that outputs an electric signal in accordance with the infrared light captured by the optical system (both not shown). A display unit 14 for displaying an image captured by the imaging unit 12 is mounted on the upper surface of the front end of the housing 39.
The peeling unit 16 includes: a frame 42 extending upward from the end of the guide rail 4a on the base 4; and an arm 44 extending from the base end in the X direction and movably coupled to the frame 42 in the Z direction. The housing 42 incorporates Z-direction moving means (not shown) for moving the arm 44 forward and backward in the Z-direction. A motor 46 is attached to the distal end of the arm 44, and a disc-shaped suction piece 48 is connected to the lower surface of the motor, and the suction piece 48 is rotatable about an axis extending in the Z direction. A plurality of suction holes are formed in the lower surface (suction surface) of the suction sheet 48, and are connected to a suction unit (not shown) through a flow path (not shown). The suction sheet 48 incorporates an ultrasonic vibration applying unit (not shown) that applies ultrasonic vibration to the lower surface.
The laser processing apparatus 2 includes a control unit (not shown) including a computer, and the control unit includes a Central Processing Unit (CPU) for performing arithmetic processing based on a control program, a Read Only Memory (ROM) for storing the control program and the like, and a Random Access Memory (RAM) for temporarily storing arithmetic results and the like. The control unit is electrically connected to the moving unit 8, the laser beam irradiation unit 10, the imaging unit 12, the display unit 14, the peeling unit 16, and the like of the laser processing apparatus, and controls the operations thereof.
The laser beam irradiation unit 10 according to the embodiment of the present invention will be described in detail with reference to fig. 2.
The laser beam irradiation unit 10 includes: a condenser 10a for irradiating a laser beam LB to a workpiece; a laser oscillator 10b that oscillates a laser beam LB; and a reflection plate 10c that guides the laser beam LB oscillated from the laser oscillator 10b to the condenser 10 a. The laser oscillator 10b includes: a laser light source 101 that oscillates a high-frequency pulse laser beam LB1 with a low output as seed light (seed light); an acoustic-optical Modulator (AOM) 102 as an thinning unit that thins out a high-frequency pulse laser beam LB1 oscillated from the laser light source 101 at a predetermined repetition frequency to generate 1 burst pulse BP from a plurality of high-frequency pulses (3 pulses in the present embodiment, hereinafter referred to as "sub-pulses"); a damper 103 that absorbs the pulsed laser light thinned out by the grating action of the AOM 102; and an amplifier 104 that amplifies the pulsed laser LB2 transmitted through the AOM 102 and composed of a burst BP including a plurality of sub-pulses.
The AOM 102 has an acousto-optic medium made of, for example, tellurite glass, and the acousto-optic medium is bonded to a piezoelectric element, not shown. When ultrasonic vibration is transmitted to the acousto-optic medium by the piezoelectric element, the acousto-optic medium acts as a grating by the photoelastic effect, and the piezoelectric element of the AOM 102 is connected to an AOM control unit 105 for generating arbitrary ultrasonic vibration. By controlling the AOM control means 105, the number of pulses of the sub-pulses that constitute the burst BP through the AOM 102 can be set to an arbitrary number. The laser light source 101, the AOM control unit 105, and the amplifier 104 are appropriately controlled by a control unit, not shown, included in the laser processing apparatus 2.
In the laser processing apparatus 2 of the present embodiment, when a wafer of GaN is produced from a GaN ingot, the laser beam irradiation unit 10 irradiates the laser beam LB generated by amplifying the pulse laser beam LB2 composed of the burst pulse BP including a plurality of sub-pulses. In order to efficiently obtain a GaN wafer by positioning the focal point of the laser beam LB at a predetermined height position where lift-off is planned inside the GaN ingot and irradiating the entire interface surface, it is preferable to appropriately determine the number of pulses of the sub-pulses constituting 1 burst pulse BP. Hereinafter, a method of determining the number of pulses of the sub-pulses constituting the 1 burst BP will be described.
As shown in fig. 3 (a), in order to produce a GaN wafer having a thickness of 150 μm from a GaN ingot 60 as a workpiece, the laser processing apparatus 2 of the present embodiment irradiates the GaN wafer with a focused laser beam positioned at a position 150 μm away from the front surface of the GaN ingot. Therefore, in order to determine the pulse number of the appropriate sub-pulse constituting 1 burst BP, laser processing is tried to be performed at the same position, and 1 laser processing mark P is formed.
Fig. 3 (b) shows a partially enlarged plan view of GaN ingot 60 subjected to laser processing in a plan view from above. A breakdown layer B for separating the GaN ingot into Ga and N is formed in the horizontal direction around the laser processing mark P formed by the laser processing. The upper layer shows a case where a burst pulse is formed by setting the number of sub-pulses constituting 1 burst pulse to 2 pulses, a case where the number of sub-pulses is 3 pulses, and a case where the number of sub-pulses is 7 pulses. As is apparent from the figure, in the case where the sub-pulse is 2 pulses, the damaged layer B extends by about 230 μm in the horizontal direction centered on the processing mark P. Similarly, it was confirmed that the destruction layer B extended by 680 μm in the case of 3 pulses of the sub-pulse and by 50 μm in the case of 7 pulses of the sub-pulse. Fig. 3 (c) shows the results of measuring the average length of the damaged layer B extending in the horizontal direction when the trial laser processing was performed between 2 and 10 pulses.
As can be understood from these results, the optimal number of pulses of the sub-pulses constituting 1 burst is 3. That is, in the case of producing a GaN wafer from a GaN ingot, if 1 burst pulse is constituted by setting 3 sub-pulses and irradiating a laser beam, when a delaminated surface is formed on an interface inside the GaN ingot, the interval of the laser beam can be enlarged to the maximum extent, and the delaminated surface from which the GaN wafer is delaminated can be efficiently produced with a smaller laser processing amount. It is also assumed that the number of sub-pulses is not 3, depending on the processing conditions for laser processing, the thickness of the GaN wafer to be produced, the quality of the GaN ingot to be processed, and the like. In this case, the pulse number of the sub-pulse that extends the longest at the interface position where the focal point is located in the damage layer by performing the laser processing as described above may be obtained and applied to the actual laser processing.
The laser processing apparatus 2 configured according to the present invention is configured substantially as described above, and a method of producing a GaN wafer using the laser processing apparatus 2 of the present embodiment will be described in detail below.
First, as shown in fig. 1, the rear surface of a GaN ingot 60 is fixed to the upper surface of a chuck table 24 as a holding unit. The fixation can be performed using, for example, an epoxy resin adhesive (holding step). After the GaN ingot is fixed on the chuck table 24, an alignment process is performed. In the alignment step, first, the chuck table 24 is moved by the moving means 8 to a position below the imaging means 12, and the imaging means 12 images the GaN ingot 60. Next, the outer periphery of GaN ingot 60 and the notch (orientation flat) formed on the outer periphery are detected from the image of GaN ingot 60 captured by imaging unit 12, and chuck table 24 is moved and rotated to align GaN ingot 60 with condenser 10a, so that laser beam LB irradiated from condenser 10a at the start of processing is set to the center position of GaN ingot 60. Next, the condenser 10a is moved in the Z-axis direction by the condensing point position adjusting means to adjust the condensing point position of the pulse laser light to a position at a predetermined depth (150 μm) from the front surface of the GaN ingot.
After the focal point position is positioned at the center position of the GaN ingot, as shown in fig. 4 (a), the laser beam LB composed of the burst pulse BP is irradiated from the condenser 10a toward the center of the GaN ingot, the chuck table 24 is rotated by the action of a motor (not shown) built in the chuck table 24, and the Y-direction moving unit 28 is operated to move the chuck table 24 in the Y direction at a predetermined speed. Thereby, the laser processing mark P formed by the irradiation of the laser beam LB is formed in a spiral shape from the center of the GaN ingot (laser beam irradiation step).
The laser beam irradiation step of the present embodiment can be performed under the following processing conditions, for example.
Wavelength of laser beam LB: 1064nm
Frequency of high-frequency pulses LB 1: 64MHz
Pulse time amplitude of the high-frequency pulse LB 1: 315fs
Pulse interval of the high-frequency pulse LB 1: 15.6ns
Repetition frequency of the laser beam LB: 100kHz
The number of sub-pulses constituting the burst BP: 3 (can be selected from 2 to 10)
Time amplitude of burst BP: 31.2ns
Average output of amplified laser beam LB: 1W
Energy per 1 burst: 1/100,000(J)
Numerical Aperture (NA): 0.8
Processing feed speed: 100mm/s
The position of the interface: 150 μm (front of distance ingot)
Transposition: 600 μm
In order to form the peeled surface with uniform quality, it is preferable to maintain the processing feed rate at a constant value when the laser beam LB is irradiated under the processing conditions. Therefore, when irradiation of the pulsed laser light is started from the center of the GaN ingot, the rotation speed at which the chuck table is rotated is set to be gradually reduced. In the embodiment shown in fig. 4 (a), the irradiation of the laser beam LB is started from the center of the GaN ingot, and the rotation unit of the chuck table 24 and the Y-direction movement unit 28 are operated to gradually form the laser processing mark P into a spiral shape toward the outside. Further, as shown in fig. 4 (b), when the laser beam LB is irradiated to form the laser processing mark P on the entire interface, the chuck table 24 may be moved in the Y direction while being linearly reciprocated in the X direction, so that the entire interface may be irradiated with the laser beam LB.
As described above, in the present embodiment, since 1 burst pulse is formed from a plurality of high-frequency pulses (sub-pulses) and the laser beam is irradiated after the pulse is amplified, the energy of 1 pulse (burst pulse) is dispersed over the time width of 1 pulse and irradiated to the interface position, and GaN is separated into Ga and N in stages inside the GaN ingot 60, whereby the delaminated surface can be formed efficiently. In particular, in the present embodiment, the number of the burst pulses is selected as the number of pulses of the sub-pulses so that the number (3) of the breakdown layers extending the longest at the interface position where the focal point of the laser beam LB is located, and therefore, when the interface is irradiated with the laser beam LB, the interval between the adjacent laser beam irradiation positions can be enlarged to the maximum. Therefore, the laser processing can be finished in a short time, and the production efficiency can be further improved.
After the laser beam irradiation step is completed, a wafer peeling step is performed. In the wafer peeling step, first, the chuck table 24 is moved by the moving unit 8 to a position below the suction sheet 48 of the peeling unit 16. Next, the arm 44 is processed by a Z-direction moving means, not shown, so that the lower surface of the suction piece 48 is brought into close contact with the upper surface of the GaN ingot 60 as shown in fig. 5. Next, the suction unit is operated to suck the lower surface of the suction sheet 48 to the upper surface of the GaN ingot 60. Next, the ultrasonic vibration applying means is operated to apply ultrasonic vibration to the lower surface of the suction sheet 48, and the motor 46 is operated to rotate the suction sheet 48. This makes it possible to separate a part of GaN ingot 60 by using the interface irradiated with the laser beam in the laser beam irradiation step as a cleaved surface, and thus to efficiently produce wafer 62 having a desired thickness (150 μm). After the GaN wafer 62 is produced, the GaN wafer is transferred to a polishing unit, not shown, provided on the base 4, the upper surface of the GaN ingot 60 is polished, and the above-described laser beam irradiation step and wafer lift-off step are sequentially repeated and performed, whereby the total amount of the discarded raw material (GaN) can be reduced, and more GaN wafers can be produced from a predetermined GaN ingot more efficiently. In the present embodiment, the wafer peeling step is automatically performed by the peeling unit 16 included in the laser processing apparatus 2, but the unit for peeling the GaN wafer is not limited to this, and the peeling step may be performed by a manual operation of an operator using a jig having a tool having an adsorption surface and a holding portion for holding the tool, for example.

Claims (1)

1. A laser processing apparatus suitable for producing a GaN wafer from a GaN ingot, the laser processing apparatus comprising:
a chuck table for holding an ingot; and
a laser beam irradiation unit which irradiates a laser beam having a wavelength which is transparent to the GaN ingot held on the chuck table,
the laser beam irradiation unit includes:
a laser oscillator that oscillates a laser beam; and
a condenser for irradiating the GaN ingot with the laser beam oscillated from the laser oscillator while locating the condensing point thereof inside the GaN ingot, and forming a fracture layer which spreads horizontally around the laser processing mark and separates the GaN ingot into Ga and N on the interface having a depth corresponding to the thickness of the GaN wafer to be produced,
the laser oscillator includes:
a laser light source that oscillates high-frequency pulse laser light;
a thinning-out unit that thins out the high-frequency pulse oscillated from the laser light source at a predetermined repetition frequency and generates 1 burst pulse using the high-frequency pulse as a sub-pulse; and
an amplifier which amplifies the generated burst,
the thinning-out section sets the number of sub-pulses that make the damage layer longest at the interface position where the focal point is located, among 2 to 10 sub-pulses calculated by laser processing performed in advance in a trial manner, to the number of sub-pulses constituting 1 burst pulse.
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